1. Field of the Invention
The present invention relates to a method of hand-over processing in which a base station to be connected to a mobile terminal is switched when the mobile terminal moves from one service area covered by one base station to another service area covered by another base station.
The present application claims priority of Japanese Patent Application No.2000-285528 filed on Sep. 20, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
In mobile communication systems such as a PHS (Personal Handy-phone System), hand-over processing is performed when a mobile terminal moves from a service area covered by one base station to another service area covered by another base station.
Conventional hand-over processing will be described by referring to FIG. 8. In FIG. 8, for example, when a mobile terminal 1 is located in a service area 4 covered by a base station 2, the mobile terminal 1 is carrying out communications with the base station 2 over a wireless communication line. If the mobile terminal 1 moves and enters a service area 5 covered by a base station 3, the mobile terminal 1 performs hand-over processing in which the base station 2 being presently connected to the mobile terminal 1 is switched to the base station 3 to which the mobile terminal 1 is to be connected next.
In the conventional hand-over processing method, communications with the mobile terminal 1 being presently operated for a telephone call are terminated on a temporary basis, in order to perform the hand-over processing to hunt another base station with which the mobile terminal 1 is newly communicated. This hand-over processing takes about 2 seconds to complete its processing, which arises a problem that communication is interrupted for about 2 seconds in the middle of the call.
To solve such the problem, hand-over processing is proposed in which high-speed hand-over processing is made possible by providing one mobile terminal with two radio wave receiving sections. In the proposed high-speed hand-over processing, when a base station is switched, while the telephone voice communication is being continued by using one of the two radio wave receiving sections, a base station to which connection of the mobile terminal is handed over is hunted by using another radio wave receiving section. When the base station to which the mobile terminal is to be connected is found, switching to the base station is done, thus obtaining an effect of shortening the time of voice interruption.
FIG. 9 is a schematic block diagram showing configurations of such the mobile terminal 1 that has two radio wave receiving sections. The mobile terminal 1 includes one radio wave receiving section made up of a wireless section 10, a synthesizer 11, and a decoder 12 and he other radio wave receiving section made up of a wireless section 20, a synthesizer 21, and a decoder 22. The mobile terminal 1 further includes a switching unit 40 used to switch data fed from the decoder 12 or decoder 22 and a switching control section 30 used to control the switching unit 40.
The switching control section 30 detects a receiving level of a radio wave that the wireless sections 10 and 20 are receiving and performs hand-over processing, as shown in a flowchart of FIG. 10, based on the receiving level.
Next, the conventional hand-over processing will be described by referring to FIG. 10.
The mobile terminal 1 is measuring, at fixed intervals, a receiving level of the radio wave transmitted from the base station being presently operated for the telephone voice communication with the mobile terminal 1. If a receiving level of a radio wave transmitted from a base station is sufficiently high, the mobile terminal 1 carries out communications with the communication line connected to the base station and performs processing of the telephone voice communication (Step 901). Here, the description will be made by assuming that the radio wave from the base station is received by the wireless section 10 and the synthesizer 11.
When the radio wave receiving level becomes lower than a fixed level (hereinafter, the fixed level being referred to as a xe2x80x9chand-over processing levelxe2x80x9d), the hand-over processing is started (Step 902). When the hand-over processing is started, base station hunting processing to hunt a base station to which connection of the mobile terminal 1 is to be handed over is performed the wireless section 20 and synthesizer 21 (Step 903). In the base station hunting processing, by selecting only base stations which can provide the receiving level being level than a fixed level xe2x80x9cDxe2x80x9d (hereinafter referred to as a xe2x80x9chand-over selection levelxe2x80x9d), candidates for a base station to which the connection of the mobile terminal 1 is to be handed over are determined. Then, when the base station to which the connection of the mobile terminal 1 is handed over is determined, the hand-over processing is performed by controlling the wireless section 20 so as to receive radio waves from the determined base station and by instructing the switching control section 30 to control the switching unit 40 so as to select data fed from the decoder 22 (Step 904).
In such the conventional hand-over processing method, though the time required for the hand-over processing can be shortened, it is necessary to set the hand-over processing level at a higher value, compared with cases of ordinary hand-over processing methods, in order to maintain excellent speech quality.
When the mobile terminal 1 moves to a region in which base stations exist sparsely, in some cases, the radio wave receiving level that the base station being presently operated for the telephone voice communication provides is below the hand-over processing level all the time. In such the case, in the conventional hand-over processing method, since the hand-over level and hand-over selection level are set as fixed values, the mobile terminal 1 always performs the base station hunting, thus causing an increase in power consumption and a shortened life of a battery.
Moreover, when a case of high speed movement of the mobile terminal 1 by a car or a like is compared with a case of low speed movement of the mobile terminal 1 on foot or a like, since a level of speech quality at which the user feels comfortable varies due to an effect of fading, the hand-over processing level which is set at the fixed values is different from the hand-over processing level that can provide an optimum speech quality.
Furthermore, when the hand-over selection level is set at the fixed value, since the hand-over selection level has to be set at a somewhat high level in order to ensure good communication quality, even if a base station is one to which the connection of the mobile terminal 1 is to be handed over, when the receiving level that the base station can provide does not reach the hand-over selection level, the base station cannot be selected as the base station to which the connection of the mobile terminal 1 is to be handed over.
As described above, the conventional hand-over processing method, since the hand-over selection level and hand-over processing level are set at the fixed value, cannot properly handle various conditions of radio waves in which the mobile terminal 1 is put, which causes degradation in speech quality and needless and wasteful hunting of the base station, and increases power consumption.
In view of the above, it is an object of the present invention to provide a method for hand-over processing in which excellent speech quality is maintained and needless and wasteful hunting of a base station is not performed by coping properly with various conditions of radio waves in which a mobile terminal is put, which can reduce power consumption.
According to a first aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a predetermined threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is to be handed over when the variation amount of the receiving level is judged to be greater than the threshold value;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
With the above configuration, whether the hand-over processing is started or not is judged based on the variation amount of the radio wave receiving level provided by the base station being presently operated for the telephone voice communication and, therefore, even if the receiving level is high at the time of the high speed movement of the mobile terminal, the hand-over processing can be started easily, thus providing optimum voice quality. Moreover, the hand-over selection level can be variable depending on the receiving level provided by the base station being presently operated for the telephone voice communication and therefore it is possible to properly cope with various conditions of radio waves in which the mobile terminal is put and thus needless base station hunting can be prevented and an increase in power consumption can be avoided, and the hand-over processing is performed whenever the hand-over is necessary and therefore telephone voice communication quality can be improved. Furthermore, a difference in the receiving level between the receiving level provided by the base station being presently operated for the telephone voice communication and the hand-over selection level is set and therefore indiscriminate and random repetition of the hand-over processing can be prevented and needless hand-over processing can be avoided.
According to a second aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of comparing a receiving level with a predetermined value, the receiving level being provided by the base station being presently operated for the telephone voice communication;
a step of measuring, at fixed intervals, the receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing, when a present receiving level provided by the base station being operated for the telephone voice communication is judged to be higher than a predetermined value, a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between the present receiving level and a receiving level measured last time;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is to be handed over when the variation amount of the receiving level is judged to be greater than the predetermined first threshold value;
a step of comparing the variation amount of the receiving level with a second threshold value which is smaller than the predetermined first threshold value, when the receiving level provided by the base station being presently operated for the telephone voice communication is judged to be lower than the predetermined value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is greater than the second threshold value;
a step of providing, in the base station hunting processing, a hand-over selection lever by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
With the above configuration, when the receiving level provided by the base station being presently operated for the telephone voice communication is higher than a predetermined level, by using, as the threshold value for the variation amount of the receiving level used to judge whether the hand-over processing is started or not, the predetermined first threshold value being a high value and, when the receiving level provided by the base station being presently operated for the telephone voice communication is lower than the predetermined level, by using, as the predetermined threshold value for the variation amount of the receiving level used to judge whether the hand-over processing is started or not, the second threshold value being lower than the first threshold value, the indiscriminate hand-over processing is not started when the receiving level provided by the base station being presently operated for the telephone voice communication is high and, therefore, needless base station hunting can be reduced without degradation of the radio wave receiving quality and, when the receiving level provided by the base station being presently operated for the telephone voice communication is low, the hand-over processing is easily started to avoid the degradation of the radio wave receiving quality.
According to a third aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of comparing a receiving level provided by the base station being presently operated for the telephone voice communication with a plurality of predetermined values;
a step of measuring, at fixed intervals, the receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication and the threshold value is determined by comparison between the present receiving level provided by the base station being operated for the telephone voice communication and the plurality of predetermined values;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is to be handed over when the variation amount of the receiving level is judged to be greater than the threshold value;
a step of providing, in the base station bunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to a fourth aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication;
a step of comparing the variation amount of the receiving level with a predetermined second threshold value when the variation amount of the receiving level is judged to be greater than the first threshold value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the predetermined second threshold value;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to a fifth aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a plurality of predetermined threshold values, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than all of the threshold values being subjected to the comparison;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to a sixth aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured a predetermined number of times before the last provided by the base station being operated for the telephone voice communication;
a step of comparing the variation amount of the receiving level with a predetermined second threshold value when the variation amount of the receiving level is judged to be greater than the first threshold value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the predetermined second threshold value;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
With the above configurations, the threshold value used in the comparison with the variation amount of the receiving level and the threshold value for the variation amount of the receiving level used to judge whether the hand-over processing is started are set an arbitrary number of times and the comparison processing can be combined and therefore finer setting is made possible.
According to a seventh aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of comparing a receiving level with a predetermined value, the receiving level being provided by the base station being presently operated for the telephone voice communication;
a step of measuring, at fixed intervals, the receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing, when a present receiving level provided by the base station being operated for the telephone voice communication is Judged to be higher than a predetermined value, a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between the present receiving level and a receiving level measured last time;
a step of comparing the variation amount of the receiving level with a predetermined second threshold value when the variation amount of the receiving level is judged to be greater than the first threshold value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the predetermined second threshold value;
a step of comparing the variation amount of the receiving level with a third threshold value which is smaller than the predetermined first threshold value, when the receiving level provided by the base station being presently operated for the telephone voice communication is judged to be lower than the predetermined value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is greater than the third threshold value;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to an eighth aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from taco different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of comparing a receiving level provided by the base station being presently operated for the telephone voice communication with a plurality of predetermined values;
a step of measuring, at fixed intervals, the receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with one or a plurality of threshold values, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication and the threshold value is determined by comparison between the present receiving level provided by the base station being operated for the telephone voice communication and the plurality of predetermined values;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is to be handed over when the variation amount of the receiving level is judged to be greater than the one or he plurality of threshold values;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to a ninth aspect of the present invention, there is provided a A hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured last time provided by the base station being operated for the telephone voice communication;
a step of starting base station hunting processing to hunt a base station to which connection of he mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the predetermined first threshold value;
a step of comparing the variation amount of the receiving level with a predetermined second threshold value when the variation amount of the receiving level is judged to be lower than the first threshold value;
a step of comparing the variation amount of the receiving level with a predetermined third threshold value when the variation amount of the receiving level is judged to be lower than the second threshold value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the third threshold value;
a step of providing, In the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
According to a tenth aspect of the present invention, there is provided a hand-over processing method for performing hand-over processing in a mobile terminal capable of simultaneously receiving radio waves from two different base stations, the hand-over processing is to switch the base stations to which a line is connected for making a telephone voice communication, the method including:
a step of measuring, at fixed intervals, a receiving level provided by the base station being presently operated for the telephone voice communication;
a step of comparing a variation amount of a receiving level with a predetermined first threshold value, the variation amount being indicative of a difference between a present receiving level and a receiving level measured Last time provided by the base station being operated for the telephone voice communication;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is handed over when the variation amount of the receiving level is judged to be greater than the predetermined first threshold value;
a step of comparing the variation amount of the receiving level with a predetermined plurality of second threshold values when the variation amount of the receiving level is judged to be lower than the first threshold value;
a step of starting base station hunting processing to hunt a base station to which connection of the mobile terminal is to be handed over when the variation amount of the receiving level is judged to be smaller than all of the plurality of second threshold values;
a step of providing, in the base station hunting processing, a hand-over selection level by adding a predetermined value greater than 0 (zero) to the present receiving level; and
a step of hunting, in the base station hunting processing, a base station whose receiving level is higher than the hand-over selection level as the base station to which connection of the mobile terminal is to be handed over.
In the foregoing, a preferable mode is one that wherein includes a step of disabling the base station hunting when the present receiving level provided by the base station being operated for the telephone voice communication is higher than the predetermined level.
With the above configurations, since, whether the hand-over processing is started or not is judged depending on whether the amount of variations in the receiving level provided by the base station being presently operated for the telephone voice communication is large or not, the quality that can provide clear reception can be maintained in the case of both the high speed movement of the mobile terminal and the low speed movement of the mobile terminal. Moreover, since the hand-over processing level is made variable depending on the variation value based on the receiving level that the base station provides, the case can be avoided in which the hunting of the base station for the hand-over is always carried out in spite of the case in which the receiving level provided by the base station is, all the time, below the hand-over processing level in regions in which base stations exist sparsely, which prevents needless base station hunting processing, thus reducing power consumption. Also, the hand-over selection level is made changeable depending on the receiving level that the base station provides and therefore the base station hunting at the optimum level is made possible and the quality that can provide clear reception is ensured. Furthermore, when the receiving level provided by the base station being presently operated for the telephone voice communication is maintained at the high level, even if variations occur in the receiving level, since the hand-over processing Is not required, needless hand-over processing is not performed, also thus contributing to reduce the power consumption.